Lubricant composition

ABSTRACT

A lubricant composition includes a perfluoropolyether as a base oil, a fluororesin as a thickener, and a polyol ester, a urea grease and a zinc dialkyldithiophosphate as additives, wherein a mass ratio of content of the perfluoropolyether to total content of the polyol ester and the urea grease ranges from 78/22 to 95/5, a mass ratio of content of the perfluoropolyether to content of the polyol ester ranges from 90/10 to 96.5/3.5, a mass ratio of content of the polyol ester to content of the urea grease ranges from 40/60 to 65/35, content of the fluororesin ranges from 15 mass % to 24 mass % based on a total amount of the lubricant composition, and content of the zinc dialkyldithiophosphate ranges from 0.5 mass % to 4 mass % based on the total amount of the lubricant composition.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of InternationalApplication No. PCT/JP2016/084911, filed on Nov. 25, 2016, which claimspriority to Japanese Patent Application No. 2015-237554, filed on Dec.4, 2015. The contents of these applications are incorporated herein byreference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to a lubricant composition, and moreparticularly relates to a lubricant composition which has sufficientfretting wear resistance, and can sufficiently inhibit leakage frombearings even when used under a high-temperature environment.

Background Art

Fluorine grease is excellent in durability at high temperatures,oxidation stability, chemical resistance, and low temperatureperformance, and is used under very harsh conditions. However, fluorinegrease is expensive because its base oil and thickener are bothfluorine-based, and, is not easily compatible with lubricating materialsincluding metal, resins, rubber and the like. Also, the use of fluorinegrease under heavy load conditions causes no oil film formation requiredfor lubrication, results in fretting wear of bearings, and causesgeneration of unusual sound, increased vibration, and the like in somecases. Moreover, such fretting wear serves as a starting point to leadto more severe damage, which may result in bearing fracture orinstrumental fracture.

In general, grease is problematic in that it is easily softened whenused under a high-temperature environment and thus easily leaks frombearings when used as a lubricant for the bearings. Such the problemcauses a decrease in the amount of grease within bearings, so as toshorten the life of the bearings.

For example, Japanese Patent Application Publication No. 2003-96480discloses a lubricating grease composition incorporatingnon-fluorine-based synthetic oil in a fluorine-based lubricant, but doesnot study the fretting wear resistance and the prevention of leakagefrom bearings upon application under a high-temperature environment.Further, Japanese Patent Application Publication No. 2004-28326discloses a grease composition prepared by mixing urea-based grease andfluorine-based grease at a mass ratio ranging from 40 to 80:60 to 20,but does not study the fretting wear resistance and insufficiently studythe prevention of leakage from bearings upon application under ahigh-temperature environment. Furthermore, Japanese Patent ApplicationPublication No. 2009-35590 discloses a grease composition withinsufficient fretting wear resistance, which is prepared by mixingnon-fluorine-based grease and fluorine-based grease, and does notsufficiently study the prevention of leakage from bearings uponapplication under a high-temperature environment.

Therefore, it is an object of the present disclosure to provide alubricant composition having sufficient fretting wear resistance andbeing capable of sufficiently inhibiting leakage from bearings even whenused under a high-temperature environment.

As a result of intensive studies, the present inventors have succeededin producing a lubricant composition having sufficient fretting wearresistance, and being capable of sufficiently inhibiting leakage frombearings even when used under a high-temperature environment, and hascompleted the present disclosure. The lubricant composition comprises aperfluoropolyether as a base oil, a fluororesin as a thickener, and apolyol ester, a urea grease, and a zinc dialkyldithiophosphate asadditives, wherein a mass ratio of content of the perfluoropolyether tototal content of the polyol ester and the urea grease ranges from 78/22to 95/5, a mass ratio of content of the perfluoropolyether to content ofthe polyol ester ranges from 90/10 to 96.5/3.5, a mass ratio of contentof the polyol ester to content of the urea grease ranges from 40/60 to65/35, content of the fluororesin ranges from 15 mass % to 24 mass %based on a total amount of the lubricant composition, and content of thezinc dialkyldithiophosphate ranges from 0.5 mass % to 4 mass % based onthe total amount of the lubricant composition.

SUMMARY

Specifically, embodiments of the present disclosure relate to thefollowing (1) to (4).

(1) A lubricant composition comprising:

a perfluoropolyether as a base oil;

a fluororesin as a thickener; and

a polyol ester, a urea grease and a zinc dialkyldithiophosphate asadditives,

wherein a mass ratio of content of the perfluoropolyether to totalcontent of the polyol ester and the urea grease ranges from 78/22 to95/5;

a mass ratio of content of the perfluoropolyether to content of thepolyol ester ranges from 90/10 to 96.5/3.5,

a mass ratio of content of the polyol ester to content of the ureagrease ranges from 40/60 to 65/35,

content of the fluororesin ranges from 15 mass % to 24 mass % based on atotal amount of the lubricant composition, and

content of the zinc dialkyldithiophosphate ranges from 0.5 mass % to 4mass % based on the total amount of the lubricant composition.

(2) The lubricant composition according to (1), wherein the fluororesinis polytetrafluoroethylene.

(3) The lubricant composition according to (1), wherein the lubricantcomposition is used for a bearing of an automobile accessory.

(4) The lubricant composition according to (2), wherein the lubricantcomposition is used for a bearing of an automobile accessory.

(5) The lubricant composition according to (3), wherein the automobileaccessory is an exhaust gas recirculation system, an electronic throttlecontrol, an electric variable timing mechanism, or a variable nozzleturbo.

(6) The lubricant composition according to (4), wherein the automobileaccessory is an exhaust gas recirculation system, an electronic throttlecontrol, an electric variable timing mechanism, or a variable nozzleturbo.

Effects of Disclosure

The lubricant composition of the present disclosure has sufficientfretting wear resistance and can sufficiently inhibit leakage frombearings even when used under a high-temperature environment, so that itcan be used as a lubricant for bearings for automobile accessories.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a schematic longitudinal sectional diagram of a testmachine when a fretting wear resistance test was conducted in Examples.Moreover, FIG. 1(b) is a schematic cross sectional diagram of the testmachine, illustrating a supporting member and a shaft alone.

FIG. 2 is a schematic sectional diagram of a test machine when a leakagetest was conducted in the Examples.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described indetail.

(Lubricant Composition)

The lubricant composition of an embodiment of the present disclosurecomprises a perfluoropolyether (hereinafter referred to as “PFPE”) as abase oil, a fluororesin as a thickener, a polyol ester, a urea greaseand a zinc dialkyldithiophosphate (hereinafter referred to as a “ZnDTP”)as additives. If necessary, various additives may further be blendedtherewith.

(Base Oil)

As PFPE to be used as a base oil, a compound represented by thefollowing general formula (1) is preferably used.RfO(CF₂O)_(x)(C₂F₄O)_(y)(C₃F₆O)_(z)Rf  (1)

wherein a CF₂O group, a C₂F₄O group and a C₃F₆O group are groupsrandomly bound in the main chain, Rf is a lower perfluoro-alkyl grouphaving 1 to 5 carbon atom, preferably 1 to 3 carbon atom, such as aperfluoromethyl group, a perfluoroethyl group, and a perfluoropropylgroup. Specifically, compounds represented by the following generalformulae (2) to (5) can be preferably used.RfO[CF(CF₃)CF₂O]_(z)Rf  (2)

wherein Rf is as defined above, and z=2 to 200. This compound isobtained by completely fluorinating a precursor generated by subjectinghexafluoropropylene to photooxidation polymerization, or by subjectinghexafluoropropylene to anionic polymerization in the presence of acesium fluoride catalyst, followed by treatment of the thus obtainedacid fluoride compound having a terminal CF(CF₃)COF group with fluorinegas.RfO[CF(CF₃)CF₂O]_(z)(CF₂O)_(x)Rf  (3)

wherein Rf is as defined above, x+z=3 to 200, and x:z=10:90 to 90:10.This compound is obtained by completely fluorinating a precursorgenerated by subjecting hexafluoropropene to photooxidationpolymerization.RfO(CF₂CF₂O)_(y)(CF₂O)_(x)Rf  (4)

wherein Rf is as defined above, x+y=3 to 200, and x:y=10:90 to 90:10,and preferably, y/x>1. This compound is obtained by completelyfluorinating a precursor generated by subjecting tetrafluoroethylene tophotooxidation polymerization.F(CF₂CF₂CF₂O)₂₋₁₀₀CF₂CF₃  (5)

This compound is obtained by subjecting 2,2,3,3-tetrafluorooxetane toanionic polymerization in the presence of a cesium fluoride catalyst,and then treating the thus obtained fluorine-containing polyether(CH₂CF₂CF₂O)_(n) with fluorine gas under ultraviolet irradiation at 160°C. to 300° C.

The above PFPE can be used singly or in mixture. The content of PFPE inthe lubricant composition of the present embodiment ranges frompreferably 61 mass % to 72 mass % in the total amount of the lubricantcomposition.

(Thickener)

The fluororesin to be used as a thickener is not particularly limited,and is preferably polytetrafluoroethylene (hereinafter referred to as“PTFE”), a tetrafluoroethylene/hexafluoropropylene copolymer(hereinafter referred to as “FEP”), or a vinylidene fluoride-propylenecopolymer. PTFE to be used here is produced through production of a PTFEhaving a number average molecular weight Mn of about 1000 to 1000000 bysubjecting tetrafluoroethylene to a process such as emulsionpolymerization, suspension polymerization, or solution polymerization,and then treating the resulting PTFE by a process such as pyrolysis,decomposition under electron beam irradiation, γ-ray irradiation, orphysical pulverization, so that the resulting PTFE has a number averagemolecular weight Mn of about 1000 to 500000. FEP to be used here isproduced through production of an FEP a number average molecular weightMn of about 1000 to 1000000 by subjecting tetrafluoroethylene andhexafluoropropylene to a process such as emulsion polymerization,suspension polymerization, or solution polymerization, and then treatingthe resultant FEP with a process such as pyrolysis, decomposition underelectron beam irradiation, γ-ray irradiation, or physical pulverization,so that the resulting FEP has a number average molecular weight Mn ofabout 1000 to 500000. In addition, molecular weights can also becontrolled using chain transfer agents upon copolymerization reaction.The thus obtained powdery fluororesin particles have generally a meanprimary particle size of about 500 μm or less. Fluororesin particles tobe used for this purpose have a mean primary particle size of preferably1.0 μm or less. The mean primary particle size of higher than 1.0 μm mayworsen oil separation at a high temperature and may deteriorate bearingtorque characteristics.

The content of the thickener in the lubricant composition of the presentembodiment ranges from 15 mass % to 24 mass %, and preferably 20 mass %to 24 mass % in the total amount of the lubricant composition. Thecontent of the thickener that is less than 15 mass % in the total amountof the lubricant composition results in a softer composition, and worseoil separation. In contrast, the content of the thickener that is higherthan 24 mass % in the total amount of the lubricant composition resultsin an excessively hard composition and deteriorated bearing torquecharacteristics.

(Additive)

The polyol ester to be used as an additive is obtained by, for example,esterification of polyhydric alcohol and monovalent carboxylic acid.Examples of polyhydric alcohol include ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, dipropylene glycol, 2-methyl-1,3-propanediol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol,1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, glycerin,trimethylolmethane, trimethylolethane, trimethylolpropane,trimethylolbutane, 1,2,6-hexanetriol, and pentaerythritol, andpreferably neopentyl glycol, and trimethylolpropane. Furthermore,examples of monovalent carboxylic acid include C₅-C₁₈ linear or branchedfatty acid, and preferably, lauric acid, palmitic acid, and stearicacid. These alcohols and carboxylic acids can be used singly or inmixture.

The urea grease to be used as an additive contains, for example, anester oil as a base oil, and a urea compound as a thickener. The baseoil may contain poly α-olefin (PAO) or a mineral oil. Specific examplesof the ester oil include a diester, a polyol ester, and an aromaticester. Examples of the aromatic ester include a trimellitic acid ester,and a pyromellitic acid ester. These aromatic esters may be used singlyor in mixture. Specific examples of the urea compound include diureacompounds such as an aliphatic diurea compound, an alicyclic diureacompound, and an aromatic diurea compound, a triurea compound, and atetraurea compound. These urea compounds can be used singly or inmixture.

The mass ratio of the content of PFPE to the total content of the polyolester and the urea grease in the lubricant composition of the presentembodiment ranges from 78/22 to 95/5. The content of PFPE that is lessthan 78 mass % based on the total content of PFPE, the polyol ester andthe urea grease, which is 100 mass %, results in a shorter bearing life.In contrast, the content of PFPE that is higher than 95 mass % based onthe total content of PFPE, the polyol ester and the urea grease, whichis 100 mass %, results in decreased fretting wear resistance.

The mass ratio of the content of PFPE to the content of the polyol esterin the lubricant composition of the present embodiment ranges from 90/10to 96.5/3.5. The content of PFPE that is less than 90 mass % based onthe total content of PFPE and the polyol ester, which is 100 mass %, maycause leakage from bearings or may shorten the bearing life when usedunder a high-temperature environment. In contrast, the content of PFPEthat is higher than 96.5 mass % based on the total content of PFPE andthe polyol ester, which is 100 mass %, results in decreased frettingwear resistance.

The mass ratio of the content of the polyol ester and the content of theurea grease in the lubricant composition of the present embodimentranges from 40/60 to 65/35. The content of the polyol ester that is lessthan 40 mass % based on the total content of the polyol ester and theurea grease, which is 100 mass %, results in decreased fretting wearresistance. In contrast, the content of the polyol ester that is higherthan 65 mass % based on the total content of the polyol ester and theurea grease, which is 100 mass %, results in leakage from bearings whenused under a high-temperature environment.

Furthermore, an example of ZnDTP to be used as an additive is ZnDTPrepresented by the following general formula (6).

[Chemical formula 1]

In the formula (6), R¹, R², R³ and R⁴ each independently denote ahydrocarbon group. Examples of such a hydrocarbon group include a linearor branched alkyl group, or aryl group, and are preferably alkyl groupsamong these groups. Also, the number of carbon atoms of a hydrocarbongroup is preferably 8 or more, and is preferably 18 or less, and furtherpreferably 12 or less. Such an alkyl group is preferably primary orsecondary, or a mixture thereof, and is more preferably secondary.

The content of ZnDTP of the present embodiment ranges from 0.5 mass % to4 mass % and preferably ranges from 1.5 mass % to 3 mass % in the totalamount of the lubricant composition. The content of ZnDTP that is lessthan 0.5 mass % in the total amount of the lubricant composition resultsin decreased fretting wear resistance. In contrast, the content of ZnDTPthat is higher than 4 mass % in the total amount of the lubricantcomposition tends to cause leakage from bearings.

The lubricant composition of the present embodiment can further beblended with additives such as an antioxidant, an anticorrosive, acorrosion inhibitor, a wear preventing agent, an oil agent, a solidlubricant, an extreme pressure agent, and a conductivity-improvingagent, as necessary.

Examples of the antioxidant include phenol-based antioxidants such as2,6-di-tert-butyl-4-methylphenol,4,4′-methylenebis(2,6-di-tert-butylphenol), amine-based antioxidantssuch as alkyldiphenylamine, triphenylamine, phenyl-α-naphthylamine,phenothiazine, alkylated phenyl-α-naphthylamine, and alkylatedphenothiazine, and furthermore, phosphoric acid-based antioxidants, andsulfur-based antioxidants.

Examples of the anticorrosive include fatty acid, fatty acid amine,alkylsulfonic acid metal salt, alkyl sulfonic acid amine salt, oxidizedparaffin, and polyoxyethylene alkyl ether.

Examples of the corrosion inhibitor include benzotriazole,benzimidazole, thiadiazole, and sodium sebacate. The blending percentageof the anticorrosive or the corrosion inhibitor ranges from preferably0.5 mass % to 5 mass % in the lubricant composition of the presentembodiment.

Examples of the wear preventing agent include phosphorus-based compoundssuch as phosphoric ester, phosphite, and phosphoric ester amine salt,sulfur compounds such as sulfides and disulfides, sulfur-based metalsalts such as a dialkyldithiophosphate metal salt, and adialkyldithiocarbamate metal salt, and chlorine compounds such aschlorinated paraffin and chlorinated diphenyl. The blending percentageof the wear preventing agent preferably ranges from 0.5 mass % to 5 mass% in the lubricant composition of the present embodiment.

Examples of the oil agent include fatty acid or its ester, higheralcohol, polyhydric alcohol or its ester, aliphatic ester, aliphaticamine, fatty acid monoglyceride, montan wax, and amide-based wax.

Examples of the solid lubricant include molybdenum disulfide, carbonblack, graphite, boron nitride, silane nitride, and melamine cyanurate.

(Method for Producing Lubricant Composition)

According to the method for producing the lubricant composition of thepresent embodiment, the lubricant composition is produced by mixing PFPEas a base oil, the fluororesin as a thickener, and ZnDTP, the polyolester and the urea grease as additives. In addition, all materials; thatis, the above base oil, thickener and additives, may be added and mixedsimultaneously, or these materials may be mixed while separately addingthem sequentially, or some of these materials may be preliminarily mixedand then these materials may be mixed finally. Moreover, in view offurther enhancing the uniformity and stability of the lubricantcomposition, the lubricant composition is preferably produced by mixingin advance the fluororesin as a thickener with PFPE as a base oil toprepare fluorine grease, and then adding ZnDTP, the polyol ester and theurea grease as additives to the fluorine grease for mixing.

Furthermore, materials are mixed in the present embodiment using athree-roll mill or a high pressure homogenizer, for example. As such athree-roll mill, a hydraulic mill is generally used.

The lubricant composition of the present embodiment contains the polyolester at a predetermined blending ratio, so as to be excellent infretting wear resistance under micro-reciprocation. Moreover, thelubricant composition of the present embodiment contains the urea greaseat a predetermined blending ratio, so as to be able to sufficientlyinhibit leakage from bearings, even when used under a high-temperatureenvironment.

The lubricant composition of the present embodiment is used for internalcombustion engines and mechanical slide units to be used around theengines in transport devices, and particularly for bearings forautomobile accessories. Examples of bearings include bearings to be usedfor peripheral accessories of automobile engines (exhaust gasrecirculation (EGR) system, electronic throttle control (ETC), electricvariable timing mechanism (VVT), variable nozzle turbo (VNT), electricfan motor, and alternator). The lubricant composition is particularlypreferably used for exhaust gas recirculation (EGR) system, electronicthrottle control (ETC), electric variable timing mechanism (VVT), andvariable nozzle turbo (VNT).

The embodiments of the present disclosure are as described above.However, the present disclosure is not limited to the above embodimentsand encompasses all aspects included in the concept of the presentdisclosure and the scope of claims, and can be varied within the scopeof the present disclosure.

EXAMPLES

Hereinafter, the present disclosure is further described in detail basedthe Examples, but, the present disclosure is not limited to theExamples.

[1] Raw Materials

<Base Oil>

(A) PFPE:

FOMBLIN M15 (Solvay Solexis, Inc.)

Above general formula (4)

Structural formula CF₃O(CF₂CF₂O)_(y)(CF₂O)_(x)CF₃ (where y/x>1)

40° C. kinematic viscosity: 90 mm²/s

<Thickener>

(b) PTFE:

Algoflon L101 (Solvay Solexis, Inc.)

Mean primary particle size 0.1 to 0.2 μm

<Additive>

(c) Polyol Ester:

Synative ES TMTC (BASF Japan)

Fatty acid ester of trimethylolpropane

40° C. kinematic viscosity: 20 mm²/s

(d) Grease Additive (Urea-Based Grease)

Urea Grease 1:

First, a predetermined amount of an aromatic ester (40° C. kinematicviscosity: 100 mm²/s, Priolube1940 Croda) was prepared as a base oil,and then divided into two portions. One portion was mixed with apredetermined amount of 4,4′-diphenylmethane diisocyanate and the otherportion was mixed with a predetermined amount of octylamine. They werefurther mixed together. The temperature of the thus obtained mixture wasincreased to 190° C., and then 4,4′-diphenylmethane diisocyanate wasreacted with octylamine, so that an aliphatic diurea compound wasgenerated. Subsequently, the compound was cooled to room temperature andkneaded twice using a three-roll mill. Urea grease 1 was obtained byblending the aromatic ester with the aliphatic diurea compound. Inaddition, the blending percentage of the aliphatic diurea compound was15 mass % in the urea grease 1.

Urea Grease 2:

Except for using, instead of the aromatic ester, a base oil mixture (40°C. kinematic viscosity: 25 mm²/s) of a diester (DOS (bis2-(ethylhexyl)sebacate, Daihachi Chemical Industry Co., Ltd.) and PAO (SpectraSyn 4,Exxon Mobil Corporation), urea grease 2 was obtained by blending analiphatic diurea compound in the base oil mixture of the diester and PAOin a manner similar to that for the urea grease 1. In addition, theblending percentage of the aliphatic diurea compound was 15 mass % inthe urea grease 2.

Urea Grease 3:

Except for generating an aromatic diurea compound by reacting4,4′-diphenylmethane diisocyanate with aniline using a polyol ester (40°C. kinematic viscosity: 150 mm²/s, Unistar H481D, NOF CORPORATION)instead of the aromatic ester, and aniline instead of octylamine, ureagrease 3 was obtained by blending the polyol ester with the aromaticdiurea compound in a manner similar to that for the urea grease 1. Inaddition, the blending percentage of the aromatic diurea compound was 15mass % in the urea grease 3.

(f) Grease Additive (Soap-Based Grease)

Lithium Soap Grease:

An oil mixture of a diester and PAO (40° C. kinematic viscosity: 25mm²/s) was blended with a lithium soap compound S-7000 (Sakai ChemicalIndustry Co., Ltd.), so that the content % in lithium soap grease was 15mass %. The resultant was kneaded twice using a three-roll mill, so asto prepare the grease.

Lithium Complex (Li-C) Soap Grease:

An oil mixture of the diester and PAO (40° C. kinematic viscosity: 25mm²/s) was blended with a lithium complex soap compound (a reactant ofhydroxystearic acid and aliphatic dicarboxylic acid and LiOH), so thatthe content % in lithium soap grease was 20 mass %. The resultant waskneaded twice using a three-roll mill, so as to prepare the grease.

Barium Complex (Ba-C) Soap Grease:

An oil mixture of the diester and PAO (40° C. kinematic viscosity: 25mm²/s) was blended with a barium complex soap compound (a reactant ofalkylamine and aliphatic dicarboxylic acid and Ba(OH)₂), so that thecontent % in barium soap grease was 30 mass %. The resultant was kneadedtwice using a three-roll mill, so as to prepare the grease.

(e) ZnDTP:

Additin RC 3180 (Rhein Chemie)

Liquid

Corrosion Inhibitor: Irgacor DSSG (BASF Japan) Sodium Sebacate

[2] Preparation of Lubricant Composition

The above base oils, thickeners and additives were added, so thatblending ratios in Tables 1 to 4 were achieved, followed by kneadingusing a three-roll mill. Thus uniform lubricant compositions wereobtained (Examples 1 to 8, and Comparative Examples 1 to 10).

[3] Test and Evaluation of Lubricant Composition

The thus obtained lubricant compositions (Examples 1 to 8, ComparativeExamples 1 to 10) were evaluated as follows. The results are shown inTables 1 to 4.

<Fretting Wear Resistance Test>

As test bearings, non-contact rubber sealed deep groove ball bearingshaving an inner diameter of 8 mm, an outer diameter of 22 mm, and awidth of 7 mm were used. The test was conducted by adding 0.15 mL ofeach lubricant composition to the test bearing in a test machine shownin FIG. 1(a), and oscillating the test machine into the directionindicated in FIG. 1(b) for 72 hours under conditions of the temperatureof the bearing outer ring of 25° C., a thrust load of 20N, a frequencyof 20 Hz, an oscillation angle of 0.3°. In addition, the thrust load wasapplied with a weight shown in FIG. 1(a).

After the completion of the test, a wear depth (μm) of the wear trackson the bearing inner ring was measured. The wear depth was determined bymeasuring the depth of the center of a part that had been worn-out tothe highest degree among wear tracks formed on the rolling surface ofthe bearing inner ring. In addition, in the Examples, a case where thewear depth was less than 1.0 μm was determined to be good.

<Leakage Test (Bearing Rotation Test)>

As test bearings, non-contact rubber sealed deep groove ball bearingshaving an inner diameter of 8 mm, an outer diameter of 22 mm, and awidth of 7 mm were used. The test was conducted by supporting a shaftwith bearings of both bearing support stands of a test machine shown inFIG. 2, adding 0.15 mL of each lubricant composition to the testbearings, and then rotating the shaft for 50 hours under conditions ofthe rotational speed of the inner ring of 3000 rpm, the temperature ofthe bearing outer ring of 180° C., and a thrust load of 39.2 N. Inaddition, the thrust load was applied by pressurization from both sidesof the shaft.

After the completion of the test, the presence or the absence of leakagefrom the bearings was visually confirmed. A case of no leakage wasdetermined to be “◯ (Good)”, and a case of the presence of leakage wasdetermined to be “x (Poor)”.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 1 Example 2 Base oil (a) PFPE 68.8 65.1 62.8 68.0 70.4   60.6Thickener (b) PTFE 23.1 21.8 21.1 22.9 23.5   20.3 Additive (c) Polyolester 2.5 5 6.5 2.5 1.5 8 (d) Urea grease 1 2.5 5 6.5 2.5 1.5 8 (e)ZnDTP 2 2 2 3.0 2   2 DSSG 1.1 1.1 1.1 1.1 1.1   1.1 (a)/(c + d)93.2/6.8 86.7/13.3 82.8/17.2 93.2/6.8 95.9/4.1 79.1/20.9 (a)/(c)96.5/3.5 92.9/7.1  90.6/9.4  96.5/3.5 97.9/2.1 88.3/11.7 (c)/(d)  50/5050/50 50/50  50/50  50/50 50/50 Fretting (wear depth [μm]) 0.5 0.5 0.40.5 1.4   0.4 Leakage ∘ ∘ ∘ ∘ ∘ x (Note) Underlined boldface numbers inthis Table indicate that they are out of the appropriate range of thepresent disclosure.

TABLE 2 Comparative Comparative Example 5 Example 2 Example 6 Example 3Example 4 Base oil (a) PFPE 65.1 Thickener (b) PTFE 21.8 Additive (c)Polyol ester 4 5 6.5 2.5 7 (d) Urea grease 1 6 5 3.5 7.5 3 (e) ZnDTP 2DSSG 1.1 (a)/(c + d) 86.7/13.3 86.7/13.3 86.7/13.3 86.7/13.3 86.7/13.3(a)/(c) 94.2/5.8  92.9/7.1  90.9/9.1  96.3/3.7  90.3/9.7  (c)/(d) 40/6050/50 65/35 25/75 70/30 Fretting (wear depth [μm]) 0.6 0.5 0.5 1.2   0.4Leakage ∘ ∘ ∘ ∘ x (Note) Underlined boldface numbers in this Tableindicate that they are out of the appropriate range of the presentdisclosure.

TABLE 3 Comparative Comparative Comparative Example 2 Example 7 Example8 Example 5 Example 6 Example 7 Base oil (a) PFPE 65.1 Thickener (b)PTFE 21.8 Additive (c) Polyol ester 5 (d) Urea grease 1 5 0 0 0 0 0 Ureagrease 2 0 5 0 0 0 0 Urea grease 3 0 0 5 0 0 0 (f) Li soap grease 0 0 05 0 0 Li—C grease 0 0 0 0 5 0 Ba—C grease 0 0 0 0 0 5 (e) ZnDTP 2 DSSG1.1 (a)/(c + d) 86.7/13.3 86.7/13.3 86.7/13.3 86.7/13.3 86.7/13.386.7/13.3 (a)/(c) 92.9/7.1  92.9/7.1  92.9/7.1  92.9/7.1  92.9/7.1 92.9/7.1  (c)/(d) 50/50 50/50 50/50 100/0   100/0   100/0   Fretting(wear depth [μm]) 0.5 0.5 0.7   0.5   0.6   0.6 Leakage ∘ ∘ ∘ x x x(Note) Underlined boldface numbers in this Table indicate that they areout of the appropriate range of the present disclosure.

TABLE 4 Comparative Comparative Comparative Example 8 Example 9 Example10 Base oil (a) PFPE  65.1  68.4 68.4  Thickener (b) PTFE   26.8 23 23   Additive (c) Polyol ester 5   7.5 5.5 (d) Urea grease 1 0 0 0   (e) ZnDTP 2 0 2   DSSG   1.1   1.1 1.1 (a)/(c + d) 92.9/7.1 90.1/9.992.6/7.4 (a)/(c) 92.9/7.1 90.1/9.9 92.6/7.4 (c)/(d) 100/0    100/0   100/0    Fretting (wear depth [μm])   0.6 2 0.5 Leakage x x x (Note)Underlined boldface numbers in this Table indicate that they are out ofthe appropriate range of the present disclosure.

As shown in Tables 1 to 3, the lubricant compositions according toExamples 1 to 8 were confirmed to be excellent in fretting wearresistance and cause no leakage from bearings even when used under ahigh-temperature environment, since the mass ratio (a)/(c+d) of thecontent of PFPE to the total content of the polyol ester and the ureagrease, the mass ratio (a)/(c) of the content of PFPE to the content ofthe polyol ester, the mass ratio (c)/(d) of the content of the polyolester to the content of the urea grease, the content (b) of PTFE, thefluororesin, and the content (e) of the zinc dialkyldithiophosphate(ZnDTP) were all within the appropriate range of the present disclosure.

In contrast, as shown in Table 1, the lubricant composition according toComparative Example 1 was found to be inferior in fretting wearresistance to the others, since the content of PFPE was higher than 95mass % based on the total content, 100 mass %, of PFPE, the polyol esterand the urea grease, and the content of PFPE was higher than 96.5 mass %based on the total content, 100 mass %, of PFPE and the polyol ester.Moreover, the lubricant composition according to Comparative Example 2was found to cause leakage from bearings when used under ahigh-temperature environment, since the content of PFPE was less than 90mass % based on the total content, 100 mass %, of PFPE and the polyolester.

Furthermore, as shown in Table 2, the lubricant composition according toComparative Example 3 was inferior in fretting wear resistance to theothers, since the content of the polyol ester was less than 40 mass %based on the total content, 100 mass %, of the polyol ester and the ureagrease. The lubricant composition according to Comparative Example 4 wasfound to cause leakage from bearings when used under a high-temperatureenvironment, since the content of the polyol ester was higher than 65mass % based on the total content, 100 mass %, of the polyol ester andthe urea grease.

Table 3 shows comparisons of grease additives, specifically betweenurea-based grease (d) and soap-based grease (f) under the sameconditions where the content was 5 mass % in the total amount of eachlubricant composition. Examples 2, 7 and 8 contained differenturea-based grease (d) additives, and Comparative Examples 5 to 7contained different soap-based grease (f) additives. In Examples 2, 7and 8, where the mass ratios (c)/(d) of the content of the polyol esterto the content of the urea grease were within the range of 40/60 to65/35, no leakage occurred regardless of urea grease types. On the otherhand, in Comparative Examples 5 to 7, where (c)/(d) was 100/0 which washigher than 65/35, all soap-based grease (f) additives were found toresult in leakage from bearings upon application under ahigh-temperature environment.

Furthermore, as shown in Table 4, the lubricant composition according toComparative Example 8 was found to cause leakage from bearings when usedunder a high-temperature environment, since the content of PTFE, thefluororesin, was higher than 24 mass % based on the total amount of thelubricant composition, and no urea grease was contained. Moreover, thelubricant composition according to Comparative Example 9 was inferior infretting wear resistance to the others and found to cause leakage frombearings when used under a high-temperature environment, since itcontained no urea grease and no zinc dialkyldithiophosphate (ZnDTP).Moreover, the lubricant composition according to Comparative Example 10was found to cause leakage from bearings when used under ahigh-temperature environment, since it contained no urea grease.

The lubricant composition of the present disclosure can be used forlubrication applications requiring heat resistance, lubricity, anddurability life.

For example, the lubricant composition can be used for internalcombustion engines and mechanical slide units to be used around suchengines in transport devices, and particularly for bearings forautomobile accessories. In particular, the lubricant composition can beused for bearings to be used for peripheral accessories of automobileengines (exhaust gas recirculation (EGR) system, electronic throttlecontrol (ETC), electric variable timing mechanism (VVT), variable nozzleturbo (VNT), electric fan motor, and alternator).

What is claimed is:
 1. A lubricant composition comprising: aperfluoropolyether as a base oil; a fluororesin as a thickener; and apolyol ester, a urea grease and a zinc dialkyldithiophosphate asadditives the urea grease comprising an ester oil and a urea compound,wherein a mass ratio of content of the perfluoropolyether to totalcontent of the polyol ester and the urea grease ranges from 82.8:17.2 to93.2:6.8; a mass ratio of content of the perfluoropolyether to contentof the polyol ester ranges from 90/10 to 96.5/3.5, a mass ratio ofcontent of the polyol ester to content of the urea grease ranges from40/60 to 65/35, content of the fluororesin ranges from 15 mass % to 24mass % based on a total amount of the lubricant composition, and contentof the zinc dialkyldithiophosphate ranges from 0.5 mass % to 4 mass %based on the total amount of the lubricant composition.
 2. The lubricantcomposition according to claim 1, wherein the fluororesin ispolytetrafluoroethylene.
 3. The lubricant composition according to claim1, wherein the lubricant composition is used for a bearing of anautomobile accessory.
 4. The lubricant composition according to claim 2,wherein the lubricant composition is used for a bearing of an automobileaccessory.
 5. The lubricant composition according to claim 3, whereinthe automobile accessory is an exhaust gas recirculation system, anelectronic throttle control, an electric variable timing mechanism, or avariable nozzle turbo.
 6. The lubricant composition according to claim4, wherein the automobile accessory is an exhaust gas recirculationsystem, an electronic throttle control, an electric variable timingmechanism, or a variable nozzle turbo.
 7. The lubricant compositionaccording to claim 1, wherein the ester oil is a diester or an aromaticester.
 8. The lubricant composition according to claim 1, wherein theester oil is different from the polyol ester.